Dbms_lob.writeappend is slow

Question

I am having a table with number , float, double of 100 columns
need to read the table value and return as blob
so i have used utl_raw.CAST_FROM_
something like this
i have used loop to read each column data type and used bind variable to insert
TYPE varColtypelist is varray(100) of NUMBER(20);
collist varColtypelist;
TYPE varColLenlist is varray(100) of number(20);
byteLenList varColLenlist;
  Select  CASE WHEN data_type ='BINARY_FLOAT' THEN 1
                  WHEN data_type ='BINARY_DOUBLE' THEN 2
                  WHEN data_type ='NUMBER' THEN 3 END  bulk collect into  collist
        from all_tab_columns where table_name=UPPER(Table_Name)
        ORDER BY COLUMN_ID ;
v_cursor := DBMS_SQL.OPEN_CURSOR;
statment :='Select all columns from mytable order by c1 desc ' and rownum between 5000 to 10000
execute immediate 'Select byte_info from my_byte_info where id=1'
bulk collect into  byteLenList ;
v_cursor := DBMS_SQL.OPEN_CURSOR;
DBMS_SQL.parse (v_cursor, statment, DBMS_SQL.native);  
FOR col_ind IN 1 .. 100--(100 is 100 columns in that table)
LOOP
  data_type := collist(col_ind);  
  if data_type =1 THEN
    DBMS_SQL.define_column  (v_cursor, col_ind, flid);
  ELSIF  data_type =2 THEN
    DBMS_SQL.define_column  (v_cursor, col_ind, dblid);
  ELSIF  data_type =3 THEN
  DBMS_SQL.define_column  (v_cursor, col_ind, nid);
  END IF;
END LOOP;
dumy := DBMS_SQL.Execute (v_cursor);
LOOP
EXIT WHEN DBMS_SQL.FETCH_ROWS (v_cursor) = 0;
FOR i IN 1..l_max LOOP 
              data_type := collist(i);  
              ncollength := byteLenList(i);         
  if data_type =1 THEN
                  BEGIN
                  DBMS_SQL.column_value (v_cursor, i, flid);
                    value :=  utl_raw.cast_from_BINARY_FLOAT( flid);
                  END;       
          end if;
  if data_type =2 THEN
                  BEGIN
                  DBMS_SQL.column_value (v_cursor, i, dblid);
                    value :=  utl_raw.cast_from_BINARY_DOUBLE( dblid);
                  END;       
          end if;
  if data_type =3 THEN
                  BEGIN
                  DBMS_SQL.column_value (v_cursor, i, nid);
                    value :=  utl_raw.CAST_FROM_BINARY_INTEGER( nid);
                  END;       
          end if;
IF nNewRecord = 0 then       
  buffer1 := utl_raw.cast_to_varchar2(dbms_lob.substr(value));
  dbms_lob.writeappend( l_out,ncollength,buffer1 );         
        End if;
   IF nNewRecord = 1 then
          nNewRecord := 0;       
          Select (utl_raw.cast_to_varchar2(dbms_lob.substr(var))) into l_out from dual;         
        end if;
end loop; 
END LOOP;
DBMS_SQL.CLOSE_CURSOR (v_cursor);
it is something like
SELECT  utl_raw.cast_to_varchar2(dbms_lob.substr(utl_raw.CAST_FROM_BINARY_INTEGER(int_column))) from mytable
SELECT  utl_raw.cast_to_varchar2(dbms_lob.substr(utl_raw.cast_from_BINARY_DOUBLE(double_coulmn))) from mytable
SELECT  utl_raw.cast_to_varchar2(dbms_lob.substr(utl_raw.cast_from_BINARY_FLOAT(float_column))) from mytable
SELECT  utl_raw.cast_to_varchar2(dbms_lob.substr(utl_raw.CAST_FROM_BINARY_INTEGER(int_column))) from mytable
SELECT  utl_raw.cast_to_varchar2(dbms_lob.substr(utl_raw.cast_from_BINARY_DOUBLE(double_coulmn))) from mytable
SELECT  utl_raw.cast_to_varchar2(dbms_lob.substr(utl_raw.cast_from_BINARY_FLOAT(float_column))) from mytable
SELECT  utl_raw.cast_to_varchar2(dbms_lob.substr(utl_raw.cast_from_BINARY_FLOAT(float_column))) from mytable
SELECT  utl_raw.cast_to_varchar2(dbms_lob.substr(utl_raw.CAST_FROM_BINARY_INTEGER(int_column))) from mytable
SELECT  utl_raw.cast_to_varchar2(dbms_lob.substr(utl_raw.cast_from_BINARY_FLOAT(float_column))) from mytable
SELECT  utl_raw.cast_to_varchar2(dbms_lob.substr(utl_raw.CAST_FROM_BINARY_INTEGER(int_column))) from mytable
SELECT  utl_raw.cast_to_varchar2(dbms_lob.substr(utl_raw.cast_from_BINARY_DOUBLE(double_coulmn))) from mytable
SELECT  utl_raw.cast_to_varchar2(dbms_lob.substr(utl_raw.cast_from_BINARY_FLOAT(float_column))) from mytable
but it is time consuming taking more time to write and apennd
can we do it in alternate way.

Answer 1

If you select a single concotenated result from table then how will you differentiate b/w datatypes of each column and how to convert them to blob.
Well that is the SAME question I ask you a month ago:
Also - if all you do is concatenate multiple values together how do you expect the result to be useful? No one will be able to tell where one value begins and the next ends.
I also ask you to do this:
Start over and tell us, in English, what BUSINESS PROBLEM you are trying to solve.
Provide a small amount (2 rows of 3 columns each) of sample data (in the form of INSERT statements, the DDL for a sample table (again - 3 columns) and show us what the result should be: 2 rows each having 1 CLOB, 1 row having 1 CLOB, etc.
What you say you are doing doesn't make much sense. That is why you were ask to explain it more fully. We can't help you if we don't know what you are really trying to do.
If you just string multiple VARCHAR2 values together that are different lengths without using some kind of delimiter it won't be meaningful.
And that seems to be just the problem you are asking about in your other thread:
https://community.oracle.com/thread/2614252?start=15&tstart=0
You caused the problem - we are asking you why are you doing that?